The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In semiconductor technology, gallium nitride (GaN) as the third generation of wide band gap semiconductor material, has characteristics of large band gap, high breakdown voltage, the two-dimensional electron gas has large electron velocity at high concentrations. Gallium nitride is used to form various integrated circuit devices, such as high power field-effect transistors, metal insulator semiconductor field effect transistors (MISFETs), high frequency transistors, and high electron mobility transistors (HEMTs).